FAS-DPD chlorine testing allows you to test higher chlorine levels than most other kits can. If you have already bought the K-2005, you can buy the K-1515. This will give you the additional test (FAS-DPD) that the K-2006 has. It comes in two sizes -- the K-1515A has 0.75 oz. reagent bottles and the 1515C has 2-oz. reagent bottles. Both kits have the same 10g. size bottle of powder.